I had a pair of Black African giants when I was younger...I'm 18 now, think i was 10 or so when I had them. Definetly awesome pets, I'll never forget the way their legs were like velcro on clothes! I housed mine in a relatively small terrarium (10 gallon, roughly) and like the other people here, fed them decaying plant matter from the yard (especially oak leaves), pieces of bark/wood, and supplemented with vegetables (lettuce and carrots were favored, though apples and grapes were popular too). They only had a heat source during winter, and it was a ~100 watt bulb.
They aren't here anymore, but I sure enjoyed looking after them. Later my father found 2 wild milipedes from the woods of our property, and though they didn't compare with the Africans they were quite large for wild VT milis. They don't do so well in captivity- neither of them lived longer than a year in the same situation.
Good luck!